Cancer is a collective term for various forms of malignant cell growth and is one of the leading causes of human deaths worldwide. Healthy cells control their own growth and will destroy themselves if they become unhealthy, while cancer cells divide and grow uncontrollably and invade nearby parts of the body. Cell division is a complex process that is normally tightly regulated. Cancer happens when problems in the genes in a cell prevent these controls from working. These problems with genes may be from damage to the gene or may be inherited. Damage to genes can come from many sources inside or outside of the cell. Faults in two types of genes are especially important: oncogenes, which drive the growth of cancer cells, and tumor suppressor genes, which prevent cancer from developing.
Cancer can be detected in a number of ways, including the presence of certain signs and symptoms, screening tests, or medical imaging. Once a possible cancer is detected it is diagnosed by microscopic examination of a tissue sample. Cancer is usually treated with chemotherapy, radiation therapy and surgery. The chances of surviving the disease vary greatly by the type and location of the cancer and the extent of disease at the start of treatment. Early detection and treatment of cancer greatly increases the chances of survival.